High-toughness corrosion-resistant hard alloy plate for progressive die as well as preparation method and application of high-toughness corrosion-resistant hard alloy plate

Abstract

The invention discloses a high-toughness corrosion-resistant hard alloy plate for a progressive die and a preparation method and application of the high-toughness corrosion-resistant hard alloy plate, and relates to the technical field of hard alloy materials. Comprising the following raw materials in parts by mass: 80-90 parts of hard phase WC; a binding phase and alloying element: 8-15 parts of Co; 2 to 8 parts of Ni; 0.5 to 2 parts of one or more of Cr3C2, CrN or metal Cr; and 0.1 to 1 part of Mo. By synergistically introducing Cr and Mo elements into a Co-Ni binding phase system and combining cold isostatic pressing densification, segmented sintering, phase regulation and control heat treatment and surface NiO / Cr2O3 double-layer passivation film construction, high hardness and high strength and toughness are achieved, meanwhile, the electrochemical corrosion resistance is remarkably improved, the crack depth after EDM machining is controlled within 40 microns, and the corrosion resistance is greatly improved. And the method is more suitable for long-term stamping working conditions of high-precision progressive dies.

Description

Technical Field

[0001] This invention relates to the field of cemented carbide materials technology, specifically to a high-strength, tough, and corrosion-resistant cemented carbide sheet for progressive dies, its preparation method, and its application. Background Technology

[0002] WC-Co based cemented carbide is widely used in progressive die blanking, bending, and deep drawing mold parts due to its high hardness, high wear resistance, and high strength. Cemented carbide sheets for progressive dies usually need to be rough-machined by wire electrical discharge machining (WEDM) or grinding wheel, and then precision ground to the final dimensions.

[0003] However, in practical applications, existing WC-Co series plates are prone to developing machining cracks with a depth of more than 50μm on the surface and subsurface after WEDM or grinding, resulting in: 1. Difficulty in ensuring the dimensional accuracy of mold parts; 2. Increased chipping and micro-chipping of cutting edges, shortening service life; 3. Rapid wear of cutting edges in long-cycle progressive stamping, making it difficult to meet the requirements of high-frequency and high-precision stamping. The main reasons for the above problems include: (1) Superposition of thermal stress and mechanical stress: WEDM discharge and grinding friction will generate high temperature locally; the thermal expansion coefficients of WC and Co differ by about 2-2.5 times, and the thermal cycle during sintering cooling and processing will generate large thermal stress between the hard phase WC and the binder phase Co; this thermal stress superimposed on the processing cutting stress will form crack sources on the surface and subsurface, promoting the initiation and expansion of microcracks into macrocracks. (2) Poor corrosion resistance of the binder phase and severe electrochemical corrosion: The binder phase of traditional WC-Co alloy is pure Co, which is easily electrochemically dissolved as an anode in the WEDM working fluid environment, forming corrosion pits on the surface and becoming a source of crack initiation; In the existing schemes to improve corrosion resistance by adding Ni and Cr, excessive Ni will reduce the hardness of the binder phase and the bonding strength of the Co / WC interface, and if Cr is unevenly distributed, it is easy to form a Cr-depleted area, resulting in pitting corrosion. (3) Unreasonable grain growth and microstructure design: Although some existing technologies introduce crystal inhibitors such as Cr3C2, uneven dispersion or rough process control still easily leads to the formation of coarse WC grains during sintering; although coarse grains can improve toughness, they will reduce the overall hardness and cause local wear to be aggravated in stamping friction, making it difficult to balance wear resistance and corrosion resistance. (4) Lack of systematic collaborative design for progressive die scenarios: Most existing technologies only optimize single indicators such as "corrosion resistance" or "fracture toughness", and usually do not provide data on WEDM crack depth and electrochemical corrosion, let alone propose a clear indicator that the crack depth after WEDM is ≤40μm. Therefore, existing technologies generally have the following problems: large crack depth (>50μm) in EDM processing, which is difficult to control; rapid edge wear, making it difficult to balance wear resistance and corrosion resistance; lack of collaborative design between the binder phase structure (fcc-Co / hcp-Co) and the surface film (NiO / Cr2O3); and lack of systematic research on the action mechanism and synergistic effect of elements such as Cr and Mo.

[0004] Based on the above problems, there is an urgent need to provide a cemented carbide sheet for progressive dies that combines high hardness, high strength, high toughness, excellent corrosion resistance, and precise control of EDM crack depth, as well as its preparation method and application, to meet the requirements of long-term stable service of high-precision progressive dies. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of large processing crack depth, insufficient corrosion resistance, and unbalanced comprehensive mechanical properties in the existing technology.

[0006] In view of this, the present invention provides a high-strength, high-toughness, and corrosion-resistant cemented carbide sheet for progressive dies, its preparation method, and its application. By synergistically introducing Cr and Mo elements into the Co-Ni binder phase system, and combining cold isostatic pressing densification, segmented sintering, phase-controlled heat treatment, and the construction of a NiO / Cr2O3 double-layer passivation film on the surface, high hardness and high strength and toughness are achieved while significantly improving electrochemical corrosion resistance. The crack depth after EDM processing is controlled to within 40 μm, making it more suitable for long-term stamping conditions of high-precision progressive dies.

[0007] A high-strength, tough, and corrosion-resistant cemented carbide sheet for progressive dies is prepared from the following raw materials in parts by weight: Hard phase WC: 80-90 parts, particle size 0.5-0.8 μm; Binder phase and alloying elements: Co: 8-15 parts; Ni: 2-8 parts, with a particle size of 0.3-0.8 μm; Cr3C2, CrN or one or more of metallic Cr: 0.5-2 parts; Mo: 0.1-1 parts.

[0008] The beneficial effects of this invention are as follows: Cr element exists in the form of carbides or nitrides, which is used to inhibit the growth of WC grains and form a Cr-rich oxide layer during sintering / oxidation; some Cr and Ni elements are dissolved in the binder phase, and form a Co-Ni-Cr solid solution with Co; Mo is mainly distributed at the WC / binder phase interface, which plays a role in interface strengthening and crack propagation resistance.

[0009] The cemented carbide sheet has the following microstructural features: 1. The volume fraction of fcc-Co phase in the binder phase is ≥70%, the volume fraction of hcp-Co phase is ≤10%, and the remainder is Ni-Co-Cr solid solution; 2. After low-temperature oxidation, a NiO / Cr2O3 double-layer passivation film with a thickness of approximately 5–15 nm is formed on the surface of the plate; 3. The material density is ≥99.4%, and the porosity is ≤0.3%.

[0010] The present invention also provides a method for preparing a high-strength, tough and corrosion-resistant cemented carbide sheet for progressive dies, comprising the following steps: (1) weighing each raw material according to the high-strength, tough and corrosion-resistant cemented carbide sheet for progressive dies; (2) Powder mixing: Add one or more of Cr3C2 powder, CrN powder or metallic Cr powder, WC powder, Co powder, Ni powder and Mo powder into a ball mill jar, use hexane as medium and paraffin as forming agent, wet ball mill, and then vacuum dry and sieve to obtain mixed powder; (3) Cold isostatic pressing: The mixed powder obtained in step (2) is loaded into the mold and cold isostatic pressing is used to obtain a compact with a density ≥99.4%; (4) Segmented sintering: The compact obtained in step (3) is sintered in a vacuum or inert atmosphere by segmented heating: first, the forming agent is removed, then densification sintering is completed, and then the compact is cooled to room temperature to obtain the plate. (5) Phase control heat treatment: The plate obtained in step (4) is heated and cooled to room temperature in order to control the ratio of fcc-Co / hcp-Co phase in the binder phase; (6) Surface treatment and oxidation passivation: The working surface of the plate after step (5) is ground and mechanically polished, and then subjected to low-temperature oxidation passivation to generate a NiO / Cr2O3 double passivation film in situ on the surface.

[0011] Furthermore, in step (2), the amount of hexane added is 0.25-0.4 mL per gram of Cr3C2 powder, CrN powder or one or more of metallic Cr powder, WC powder, Co powder, Ni powder and Mo powder, and the amount of paraffin added is 0.8-2.0% of the total mass of Cr3C2 powder, CrN powder or one or more of metallic Cr powder, WC powder, Co powder, Ni powder and Mo powder.

[0012] Furthermore, in step (2), the ball milling speed is 70-100 r / min and the ball milling time is 20-32 h.

[0013] Furthermore, in step (2), the process parameters for vacuum drying are: temperature of 50-80℃, drying time of 20-40min, vacuum degree of <100KPa, and passing through a 40-80 mesh sieve.

[0014] Furthermore, in step (3), the pressure of the cold isostatic pressing process is 200-300 MPa, and the holding time is 5-15 min.

[0015] Further, in step (4), the molding agent is removed by holding at 400-600℃ for 20-50 min, and densification sintering is completed by holding at 1300-1450℃ for 30-60 min. Then, the temperature is cooled to room temperature at a rate of 15-25℃ / s.

[0016] Further, in step (5), the board obtained in step (4) is heated to 900-1000℃ and kept at that temperature for 1-2 hours, and then cooled to room temperature at a rate of ≤10℃ / s.

[0017] Further, in step (6), the working surface of the plate after step (5) is ground and mechanically polished to make the surface roughness Ra≤0.05μm, and then subjected to low-temperature oxidation passivation at 200-300℃ for 1-2 h to generate a NiO / Cr2O3 double-layer passivation film in situ on the surface.

[0018] The present invention also provides the application of the high-strength, tough, and corrosion-resistant cemented carbide sheet for progressive dies or the method thereof in the manufacture of high-precision progressive stamping die parts in the automotive, electronics, and electrical appliance fields.

[0019] The sheet material obtained by this invention has the following performance indicators: Vickers hardness HV30: approximately 1420–1480; transverse tensile strength TRS: ≥3985 MPa, up to a maximum of 4320 MPa; fracture toughness KIC: ≥13.0 MPa·m 1 / 2 ; After machining under uniform WEDM conditions, the average crack depth is ≤40 μm (the lowest in a typical example is approximately 27.2 μm); in the potentiodynamic testing under a cutting fluid simulation environment, the corrosion potential Ecorr is approximately -203 to -176 mV, and the corrosion current density icorr is (5.2 to 3.2) × 10⁻⁶ mV. -6 A / cm².

[0020] Compared with the prior art, the present invention has the following beneficial effects: 1. Cr and Mo synergistically enhance the bonding between the binder phase and the interface, balancing corrosion resistance and toughness: Cr exists partly in the form of Cr3C2 / CrN, which is used to inhibit WC grain growth and provide a Cr-rich source for subsequent surface oxidation, and partly in the form of metallic Cr dissolved into the Co-Ni binder phase; Mo is added in the range of 0.1-1 parts, preferentially enriched at the WC / binder phase interface, and strengthens the interface bonding strength and the resistance to crack propagation through solid solution and micro-area precipitation. 2. Precise control of fcc-Co / hcp-Co phase structure through phase modulation heat treatment: Through phase modulation heat treatment with holding at 900-1000℃ and cooling at ≤10℃ / s, the fcc-Co content in the binder phase is ≥70% and hcp-Co ≤10%, which improves toughness and reduces crack sensitivity caused by brittle phase while ensuring strength. 3. Constructing a NiO / Cr2O3 bilayer passivation film significantly improves electrochemical corrosion behavior: Through the process of "polishing at a low temperature of 200-300℃ and oxidation passivation", a stable and dense NiO / Cr2O3 bilayer film is formed. In the cutting fluid simulation solution, the corrosion potential shifts positively by about 40-70 mV and the corrosion current density decreases by about 40-50%, which significantly inhibits corrosion pits and secondary cracks caused by galvanic cell corrosion under WEDM conditions. 4. High-density CIP process combined with multi-component binder phase to precisely control EDM crack depth: The density is ≥99.4% by cold isostatic pressing at 200-300 MPa. Under the same WEDM conditions, the average crack depth of the plate of this invention is 27.2–38.5m, while the traditional WC-Co alloy generally exceeds 50 μm and has no quantitative index. 5. Provide systematic single-variable comparative experiments to verify the necessity and synergy of the invention points: For key invention points such as binder phase composition, phase control heat treatment, surface passivation, CIP pressure and Mo addition amount, design multiple sets of single-variable comparative experiments to quantitatively demonstrate that each improvement is not only effective on its own, but also synergistic with other measures, thereby improving the credibility and inventiveness of the invention. Attached Figure Description

[0021] Figure 1 This is a crack depth diagram of the cemented carbide wire cutting in Example 1. Detailed Implementation

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Example 1 (1) Weigh the raw materials: WC powder: 81 parts, particle size 0.5μm; Co powder: 10 parts; Ni powder: 2 parts, particle size 0.8μm; Cr3C2 powder: 1.5 parts; Mo powder: 0.5 parts; (2) Powder mixing: Cr3C2 powder, WC powder, Co powder, Ni powder and Mo powder are added to a ball mill jar. The amount of hexane added is 0.38 mL of hexane per gram of Cr3C2 powder, WC powder, Co powder, Ni powder and Mo powder. The amount of paraffin added is 2.0% of the total mass of Cr3C2 powder, WC powder, Co powder, Ni powder and Mo powder. The mixture is wet ball milled at 75 r / min for 24 h. After vacuum drying and sieving, the process parameters for vacuum drying are 60℃ temperature, 30 min drying time, 50 kPa vacuum degree, and passing through a 60 mesh sieve to obtain mixed powder. (3) Cold isostatic pressing: The mixed powder obtained in step (2) is loaded into the mold and cold isostatic pressing is used to hold the pressure at 200 MPa for 10 min to obtain a compact with a density of 99.4%. (4) Segmented sintering: The compact obtained in step (3) is sintered in segments under an argon atmosphere, the molding agent is removed by holding at 500℃ for 20 min, and densification is completed by holding at 1400℃ for 45 min. Then, it is cooled to room temperature at a rate of 20℃ / s to obtain the plate. (5) Phase control heat treatment: Heat the plate obtained in step (4) to 950℃ and hold for 1.5h, then cool to room temperature at a rate of 8℃ / s; (6) Surface treatment and oxidation passivation: The working surface of the plate after step (5) is ground and mechanically polished to make the surface roughness Ra=0.03μm. Then, it is kept at 250℃ for 1.5 h for low-temperature oxidation passivation to generate a NiO / Cr2O3 double passivation film in situ on the surface.

[0024] The performance indicators of the obtained cemented carbide sheet are: hardness 1420 HV, transverse tensile strength 3985 MPa, and fracture toughness 13.1 MPa·m. 1 / 2 Corrosion resistance: Corrosion potential Ecorr is -203mV, corrosion current density icorr is 5.2×10⁻⁶ mV. -6 A / cm 2 After EDM processing, the average crack depth was 38.5 μm. Scanning electron microscopy analysis showed that fcc-Co accounted for 75% of the binder phase, hcp-Co accounted for 8%, and the remainder was Ni-Co-Cr solid solution, with a NiO / Cr2O3 double-layer passivation film formed on the surface.

[0025] Example 2 (1) Weigh the raw materials: WC powder: 85 parts, particle size 0.8μm; Co powder: 12 parts; Ni powder: 3 parts, particle size 0.5μm; Cr3C2 powder: 1.0 part; CrN powder: 0.7 parts; Mo powder: 0.8 parts; (2) Powder mixing: Cr3C2 powder, CrN powder, WC powder, Co powder, Ni powder and Mo powder are added to a ball mill jar. The amount of hexane added is 0.30 mL of hexane per gram of Cr3C2 powder, WC powder, Co powder, Ni powder and Mo powder. The amount of paraffin added is 1.5% of the total mass of Cr3C2 powder, WC powder, Co powder, Ni powder and Mo powder. The mixture is wet ball milled at 800 r / min for 22 h. After vacuum drying and sieving, the process parameters for vacuum drying are 70℃ temperature, 25 min drying time, 60 kPa vacuum degree, and passing through a 70 mesh sieve to obtain mixed powder. (3) Cold isostatic pressing: The mixed powder obtained in step (2) is loaded into the mold and cold isostatic pressing is used to hold the pressure at 200MPa for 15 min to obtain a compact with a density of 99.6%. (4) Segmented sintering: The compact obtained in step (3) is sintered in a vacuum or inert atmosphere, heated in segments, and the molding agent is removed by holding at 450℃ for 25 min. The densification sintering is completed by holding at 1420℃ for 50 min. Then, it is cooled to room temperature at a rate of 15℃ / s to obtain the plate. (5) Phase control heat treatment: The plate obtained in step (4) is heated to 980℃ and held for 2 h, and then cooled to room temperature at a rate of 6℃ / s; (6) Surface treatment and oxidation passivation: The working surface of the plate after step (5) is ground and mechanically polished to make the surface roughness Ra=0.04μm. Then, it is kept at 280℃ for 222 h for low-temperature oxidation passivation to generate a NiO / Cr2O3 double passivation film in situ on the surface.

[0026] The performance indicators of the obtained cemented carbide sheet are: hardness 1450 HV, transverse tensile strength 4150 MPa, and fracture toughness 13.5 MPa·m. 1 / 2 Corrosion resistance: Corrosion potential Ecorr is -188mV, corrosion current density icorr is 4.4×10⁻⁶. -6 A / cm 2 After EDM processing, the crack depth was 31.4 μm. Scanning electron microscopy analysis showed that fcc-Co accounted for 72% of the binder phase, hcp-Co accounted for 9%, and the remainder was Ni-Co-Cr solid solution. A NiO / Cr2O3 double-layer passivation film could still be formed on the surface.

[0027] Example 3 (1) Weigh the raw materials: WC powder: 88 parts, particle size 0.6μm; Co powder: 15 parts; Ni powder: 4 parts, particle size 0.3μm; CrN powder: 1.0 part; metallic Cr powder: 0.4 parts; Mo powder: 0.5 parts; (2) Powder mixing: CrN powder, metallic Cr powder, WC powder, Co powder, Ni powder and Mo powder are added to a ball mill jar. The amount of hexane added is 0.35 mL of hexane per gram of Cr3C2 powder, WC powder, Co powder, Ni powder and Mo powder. The amount of paraffin added is 1.8% of the total mass of Cr3C2 powder, WC powder, Co powder, Ni powder and Mo powder. The mixture is wet ball milled at 90 r / min for 28 h. After vacuum drying and sieving, the process parameters for vacuum drying are 60℃ temperature, 25 min drying time, 70 kPa vacuum degree, and passing through an 80 mesh sieve to obtain mixed powder. (3) Cold isostatic pressing: The mixed powder obtained in step (2) is loaded into the mold and cold isostatic pressing is used to hold the pressure at 280 MPa for 15 min to obtain a compact with a density of 99.7%. (4) Segmented sintering: The compact obtained in step (3) is sintered in a vacuum or inert atmosphere, heated in segments, and the molding agent is removed by holding at 550℃ for 30 min. The densification sintering is completed by holding at 1380℃ for 40 min. Then, it is cooled to room temperature at a rate of 25℃ / s to obtain the plate. (5) Phase control heat treatment: The plate obtained in step (4) is heated to 920℃ and held for 1 h, and then cooled to room temperature at a rate of 10℃ / s to control the ratio of fcc-Co / hcp-Co phase in the binder phase, so that the volume fraction of fcc-Co phase is not less than 70% and the volume fraction of hcp-Co phase is not more than 10%; (6) Surface treatment and oxidation passivation: The working surface of the plate after step (5) is ground and mechanically polished to make the surface roughness Ra=0.02μm. Then, it is kept at 220℃ for 1 h for low-temperature oxidation passivation to generate a NiO / Cr2O3 double passivation film in situ on the surface.

[0028] The performance indicators of the obtained cemented carbide sheet are: hardness 1480 HV, transverse tensile strength 4320 MPa, and fracture toughness 14.1 MPa·m. 1 / 2 Corrosion resistance: Corrosion potential Ecorr is -176mV, corrosion current density icorr is 3.2×10⁻⁶ mV. -6 A / cm 2 The crack depth after EDM processing was 27.2 μm (see appendix). Figure 1 Scanning electron microscopy analysis showed that fcc-Co accounted for 73% of the binder phase, hcp-Co accounted for 7%, and the remainder was Ni-Co-Cr solid solution. A NiO / Cr2O3 double-layer passivation film could still be formed on the surface.

[0029] Comparative Example 1: The binder phase contains only Co This comparative example is used to compare and verify the effects of whether the binder phase contains Ni, Cr, and Mo on the overall properties of the alloy and the depth of EDM cracks.

[0030] (1) Weigh the raw materials: WC powder: 88 parts, particle size 0.6μm; Co powder: 12 parts; (2) Powder mixing: WC powder and Co powder were added to a ball mill jar. The amount of hexane added was 0.35 mL per gram of total WC powder and Co powder, and the amount of paraffin added was 1.8% of the total mass of WC powder and Co powder. The mixture was wet-milled at 90 r / min for 28 h, and then vacuum-dried and sieved. The vacuum drying process parameters were: temperature 60℃, drying time 30 min, vacuum degree 50 kPa, and sieve through a 60-mesh sieve. The mixed powder was obtained. Steps (3)-(6) are the same as in Example 3.

[0031] Comparative Example 2: Elimination of Phase Modulation Heat Treatment This comparative example is used to compare and verify the effects of phase modulation heat treatment on the phase structure of the binder phase and the depth of EDM cracks.

[0032] Compared with Example 3, except that the phase control heat treatment in step (5) was not performed, the working surface of the plate obtained in step (4) was directly ground and mechanically polished to make the surface roughness Ra=0.02μm, and then low-temperature oxidation passivation was performed by holding at 220℃ for 1 h. The other steps were the same as in Example 3.

[0033] The Vickers hardness (HV30), transverse fracture strength (TRS), fracture toughness (KIC), crack depth and potentiodynamic polarization of the samples prepared in Example 3, Comparative Example 1 and Comparative Example 2 were tested. The results are shown in Table 1.

[0034] Table 1. Effects of multi-component binder phase and phase-modulated heat treatment on alloy properties (comparison of single variables)

[0035] As shown in Table 1, under the same sintering and phase-modulation heat treatment conditions, compared with Comparative Example 1 which only used Co as a binder phase, Example 3, by introducing Ni, Cr, and Mo into the binder phase, increased the hardness from 1350 HV to 1480 HV, the transverse fracture strength from 3600 MPa to 4320 MPa, and the fracture toughness from 12.5 MPa·m. 1 / 2 Increased to 14.1 MPa·m 1 / 2 Meanwhile, the EDM crack depth decreased significantly from 66.8 μm to 27.2 μm, and the corrosion current density icorr decreased from 10.6 × 10⁻⁶. -6 A / cm 2 Reduced to 3.2×10 -6 A / cm 2 This indicates that the multi-component synergistic binder phase significantly improves the strength, toughness, and corrosion resistance of the material, and effectively reduces the depth of wire-cut cracks.

[0036] With the same binder phase chemical composition, compared to Comparative Example 2 without phase-modified heat treatment, Example 3, through phase-modified heat treatment at 920 °C, increased the transverse fracture strength from 3920 MPa to 4320 MPa, reduced the EDM crack depth from 38.7 μm to 27.2 μm, and decreased the corrosion current density icorr from 5.8 × 10⁻⁶ MPa. -6 A / cm² decreased to 3.2×10 -6 A / cm 2 This indicates that phase-controlled heat treatment, by adjusting the ratio of fcc-Co / hcp-Co phases, further optimized the phase structure of the binder phase, significantly improving strength and toughness while maintaining high hardness and reducing crack sensitivity.

[0037] Comparative Example 3: Polishing only, without passivation film This comparative example is used to compare and verify the effect of surface oxidation and passivation treatment on the electrochemical properties of the alloy and the depth of EDM cracks.

[0038] Compared with Example 2, except that step (6) is replaced with surface treatment: the working surface of the plate after step (5) is ground and mechanically polished to make the surface roughness Ra=0.04μm. The other steps are the same as in Example 2.

[0039] The Vickers hardness, EDM crack depth and potentiodynamic polarization of the samples from Example 2 and Comparative Example 3 were tested, and the results are shown in Table 2.

[0040] Table 2. Effect of NiO / Cr2O3 double-layer passivation film on alloy properties (comparison of single variables)

[0041] As shown in Table 2, under the condition that the composition of the cemented carbide matrix and the internal process are exactly the same, Example 2, by performing a low-temperature oxidation passivation treatment at 280 ℃ on the basis of polishing, after forming a NiO / Cr2O3 double-layer passivation film on the surface, reduced the EDM crack depth from 58.6 μm in Comparative Example 3 to 31.4 μm, a reduction of approximately 87%; the corrosion potential Ecorr increased from -345 mV to -188 mV, a positive shift of approximately 157 mV; and the corrosion current density icorr increased from 8.7 × 10⁻⁶ mV to 8.7 × 10⁻⁶ mV. -6 A / cm 2 Reduced to 4.4×10 -6 A / cm 2 This indicates that the surface passivation film significantly improves the stability of the material in corrosive environments and slows down the corrosion rate.

[0042] As can be seen from the above results, by constructing a NiO / Cr2O3 double-layer passivation film on the surface of cemented carbide sheet, the present invention can effectively inhibit the corrosion of the galvanic cell formed by the cutting fluid and the binder phase during the wire EDM process, reduce the initiation of corrosion pits and microcracks, and significantly reduce the EDM crack depth and cutting edge wear rate while basically maintaining the hardness, which is beneficial to improving the service life of progressive dies.

[0043] Comparative Example 4: Reducing Cold Isostatic Pressure This comparative example is used to compare and verify the effect of density changes caused by different cold isostatic pressing pressures on alloy properties.

[0044] Compared with Example 1, except for step (3) cold isostatic pressing: the mixed powder obtained in step (2) is loaded into the mold, and the cold isostatic pressing process is used to hold the pressure at 100 MPa for 10 min to obtain a compact with a density of 98.5%; the other steps are the same as in Example 2.

[0045] The density, porosity, Vickers hardness HV30, transverse fracture strength TRS, fracture toughness KIC and EDM crack depth of the samples of Example 1 and Comparative Example 4 were tested, and the results are shown in Table 3.

[0046] Table 3. Effect of cold isostatic pressing density on alloy properties (comparison of single variables)

[0047] As shown in Table 3, when the cold isostatic pressing pressure increased from 100 MPa to 200 MPa, the compaction density of the compact increased from 98.5% to 99.4%, and the porosity decreased from 1.1% to 0.3%. Under the same alloy composition and subsequent processing conditions, the transverse fracture strength of Example 1 increased from 3580 MPa to 3985 MPa, and the fracture toughness increased from 12.2 MPa·m. 1 / 2 Increased to 13.1 MPa·m 1 / 2 The EDM crack depth decreased from 52.7 μm to 38.5 μm, a reduction of more than 25%.

[0048] The above results demonstrate that the high-density structure obtained by high-pressure cold isostatic pressing can significantly reduce internal porosity and other defects, lower the crack initiation source, and achieve higher strength and toughness and a smaller EDM crack depth while ensuring the same alloy composition and phase structure. Therefore, high-density cold isostatic pressing is one of the important technological foundations for achieving the goal of "EDM crack depth ≤ 40 μm" in this invention.

[0049] Comparative Example 5: Mo-free This comparative example is used to compare and verify the effects of adding Mo on the alloy's strength, toughness, and EDM crack depth.

[0050] (1) Weigh the raw materials: WC powder: 81.5 parts, particle size 0.5μm; Co powder: 10 parts; Ni powder: 2 parts, particle size 0.8μm; Cr3C2 powder: 1.5 parts; (2) Powder mixing: Cr3C2 powder, WC powder, Co powder and Ni powder are added to a ball mill jar. The amount of hexane added is 0.38 mL of hexane per gram of Cr3C2 powder, WC powder, Co powder and Ni powder. The amount of paraffin added is 2.0% of the total mass of Cr3C2 powder, WC powder, Co powder and Ni powder. The mixture is wet-milled at 75 r / min for 24 h. After vacuum drying and sieving, the process parameters for vacuum drying are 70℃, drying time is 25 min, vacuum degree is 60 kPa, and the mixture is passed through a 70 mesh sieve to obtain mixed powder. Steps (3)-(6) are the same as in Example 1.

[0051] The Vickers hardness (HV30), transverse fracture strength (TRS), and EDM crack depth of the samples from Example 1 and Comparative Example 5 were tested, and the results are shown in Table 4.

[0052] Table 4. Effects of Mo additives on alloy properties (comparison of single variables)

[0053] As shown in Table 4, under the same composition and process conditions, the addition of appropriate amount of Mo does not significantly change the hardness of the alloy, but it can increase the transverse fracture strength from 3700 MPa to 3985 MPa and reduce the EDM crack depth from 64.1 μm to 38.5 μm. This indicates that Mo is beneficial to enhance the bonding of WC / binder phase interface, inhibit crack initiation and propagation, and further improve the crack resistance of the alloy while maintaining high hardness.

[0054] Conclusion: Through the above examples and single-variable comparative examples, it is clear that: 1. The synergistic introduction of Cr and Mo not only improves corrosion resistance, but also achieves improvements in hardness through interfacial strengthening and phase structure regulation. A comprehensive balance between strength and toughness.

[0055] 2. A synergistic process system consisting of phase-controlled heat treatment, surface NiO / Cr2O3 passivation, and high-density CIP ensures high hardness while keeping the EDM crack depth within 40 μm. 3. All key technical features have been verified through single-variable comparative experiments, and have clear technical effect correspondence and mechanism of action, which can fully support the creativity and significant progress of this invention compared with the prior art.

[0056] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A high-strength, tough, and corrosion-resistant cemented carbide sheet for progressive dies, characterized in that, Prepared according to parts by weight, including the following parts by weight: Hard phase WC: 80-90 parts, particle size 0.5-0.8 μm; Binder phase and alloying elements: Co: 8-15 parts; Ni: 2-8 parts, particle size 0.3-0.8μm; Cr3C2, CrN or one or more of metallic Cr: 0.5-2 parts; Mo: 0.1-1 part.

2. A method for preparing a high-strength, tough, and corrosion-resistant cemented carbide sheet for progressive dies, characterized in that, The steps include: (1) Weighing each raw material according to the high-strength, tough, corrosion-resistant hard alloy plate for progressive dies as described in claim 1; (2) Powder mixing: Add one or more of Cr3C2 powder, CrN powder or metallic Cr powder, WC powder, Co powder, Ni powder and Mo powder into a ball mill jar, use hexane as medium and paraffin as forming agent, wet ball mill, and then vacuum dry and sieve to obtain mixed powder; (3) Cold isostatic pressing: The mixed powder obtained in step (2) is loaded into the mold and cold isostatic pressing is used to obtain a compact with a density ≥99.4%; (4) Segmented sintering: The compact obtained in step (3) is sintered in a vacuum or inert atmosphere by segmented heating: first, the forming agent is removed, then densification sintering is completed, and then the compact is cooled to room temperature to obtain the plate. (5) Phase control heat treatment: Heat the plate obtained in step (4) and cool it to room temperature; (6) Surface treatment and oxidation passivation: The working surface of the plate after step (5) is ground and mechanically polished, and then subjected to low-temperature oxidation passivation to generate a NiO / Cr2O3 double passivation film in situ on the surface.

3. The method for preparing a high-strength, tough, and corrosion-resistant cemented carbide sheet for progressive dies according to claim 2, characterized in that, In step (2), the amount of hexane added is 0.25-0.4 mL per gram of Cr3C2 powder, CrN powder or one or more of metallic Cr powder, WC powder, Co powder, Ni powder and Mo powder, and the amount of paraffin added is 0.8-2.0% of the total mass of Cr3C2 powder, CrN powder or one or more of metallic Cr powder, WC powder, Co powder, Ni powder and Mo powder. The ball milling speed is 70-100 r / min and the ball milling time is 20-32 h.

4. The method for preparing a high-strength, tough, and corrosion-resistant cemented carbide sheet for progressive dies according to claim 2, characterized in that, In step (2), the process parameters for vacuum drying are: temperature 50-80℃, drying time 20-40min, vacuum degree <100KPa, and passing through a 40-80 mesh sieve.

5. The method for preparing a high-strength, tough, and corrosion-resistant cemented carbide sheet for progressive dies according to claim 2, characterized in that, In step (3), the pressure of the cold isostatic pressing process is 200-300 MPa, and the holding time is 5-15 min.

6. The method for preparing a high-strength, tough, and corrosion-resistant cemented carbide sheet for progressive dies according to claim 2, characterized in that, In step (4), the molding agent is removed by holding at 400-600℃ for 20-50 min, and densification sintering is completed by holding at 1300-1450℃ for 30-60 min. Then, the temperature is cooled to room temperature at a rate of 15-25℃ / s.

7. The method for preparing a high-strength, tough, and corrosion-resistant cemented carbide sheet for progressive dies according to claim 2, characterized in that, In step (5), the board obtained in step (4) is heated to 900-1000℃ and kept at that temperature for 1-2 hours, and then cooled to room temperature at a rate of ≤10℃ / s.

8. The method for preparing a high-strength, tough, and corrosion-resistant cemented carbide sheet for progressive dies according to claim 2, characterized in that, In step (6), the working surface of the plate after step (5) is ground and mechanically polished to make the surface roughness Ra≤0.05μm, and then subjected to low-temperature oxidation passivation at 200-300℃ for 1-2 h to generate a NiO / Cr2O3 double passivation film in situ on the surface.

9. The application of the high-strength, tough, corrosion-resistant cemented carbide sheet for progressive dies as described in claim 1 or the method as described in any one of claims 2-8 in the manufacture of high-precision progressive stamping die parts in the automotive, electronics, and electrical appliance fields.

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